Collagen fiber masses and methods of making the same



April 26, 1960 J. H. HIGHBERGER Er'm.

COLLAGEN FIBER MASSES AND METHODS OF MAKING THE SAME Filed Oct. 22. 1957 Soluble Young Calfskin, Colla en Fiber Animal Skin, Collaqensource MammaIinnSkln Trimmings Scarce ''Ifimminqs,

Wash, Chemical, treatment, e.g. Mince wllh Formaldehqdepr other limited tannin Preliminary Subdivision Mixture at pHZ4.5 l::l Mix with water and beat] Hold. to permit Collagen at least Aqueous suspension purtiallg to dissolve of coma? en Fibers Leuiqate I I M1,. P I Nubb Past Colla e Ma n in fess msan s olutior uncgs'soluedcollagen a) Hbe M ILumPsbwmte Lfi l fl WaterloWosfe Coolto O'to s'cI NQOH H M St E0 qiogpl-lofqztofi NH 0H 00 o 0 I flermucmg wllhfiber QEAEI Asfllt l0 giue N c Loosened Mass g?% M1 50 of Collac en Fibers ft mix-m KCLelc. (excluding with fiber) fl bq bm ollagen preopltohrlg salts I Knead I I Collagen solution containing I added collagen fibers I Shape I Sheet or other shape ofmixtm'e I Gel containing Collagen meg Remove Liquid I Optional fanning and finishing Ell Skin-like or Leothen'like Moterlal Coot opfionol Surface e w a@ to above 5 eq. (am-31C.) Collagen precipitates Inventors John H Highbezger Roberf/l.

{imam Unite COLLAGEN FIBER MASSES AND METHODS MAKING THE SAME John H. Highberger, Marblehead, and Robert A. Whitmore, Beverly, Mass., assignors to United Shoe Machinery Corporation, Flemington, .N.J., a corporation of New Jersey Application ()ctober 22, 1957, Serial No. 691,728

.11 Claims. .(Cl. 106-155) This invention relates to an improvement in thepreparation of collagen fiber masses, particularly to the preparation of sheet material convertible to leather-like con dition.

.Skin and leather are composed of fibers of a protein called collagen. Thesefibers arearranged in a randomly interwoven three-dimensional network, and the ultiskins from which leather is prepared are irregular in shape and thickness so that there is a highpercentage of waste. The waste material has been of very little value and has been disposed of inzsuch uses as fertilizers or has been used in making such .products as leather board, that is an imitation leather material in which the scraps are pasted and pressed together into sheets. These leather board sheets lack the interwoven three-dimensional network which gives to .leather its strength and other desirable properties.

Efforts have been made to develop a sheet material from the fibers of skin material by swelling the skin, mechanically breaking down .the swollen skin and forming the resultant paste into sheets or threads. In these efforts, the net effect has been to degrade thecollagen of the skin to an extent that portions of it are converted into glue which holds other ,portions' together, This material has a hard, non-fibrous feel asrnightbe expected due to the glued together nature of the product; and the product is not a randomly interwoven three-dimensional network of fibers having the character of leather.

In our earlier U.S. application Serial No. 554,557, filed December 21, 1955, entitledlmprovements in C01- lagen Fiber Masses and -Methods of Making the Same, of which the present application is a continuation-linpart, there is disclosed a process for making a skin-like or leather-like material by dissolving natural skin material to form a collagen solution and reprecipitation of the dissolved collagen in the "form of true collagen fibrous material. In one form of theprocess disclosed, undissolved collagen fibers remaining after treatment of theskin to dissolve the collagen, 'or separately prepared and added to the collagen solution, integrate with the collagen fibers formed by precipitation of dissolved .collagen to form, a network-of collagen fibers closely resembling animal skin. This skin-like material is convertible to a leather-like product by the action of tanning agents. 7 i

In the process disclosed in the above-mentioned application some difiiculty arose inpreparing undissolved collagen fibrous material in a form useful for cooperation with the dissolved collagen. That is, the separation of hide or skin material into fibers resulted in a fiber dis- States Patent persion which included clumpsof undispersed or entangled collagen fibers 'and large bundles of fibers which needed further subdivision for most effective cooperation with the collagen solution prior to reconstitution of collagen fibers. Also, difiiculty was encountered in dissolving collagen to provide a high dissolved solids content collagen solution for combination with the undissolved collagen fibers to form a strongly knit together fibrous sheet.

It is a feature of the present invention to provide an improved method for making a more strongly knit together skin-like material through chemically modifying raw material to provide a fiber product particularly adapted for combining with a high dissolved solids content collagen solution whichwill combine with the fibers from the modified material to give more effective knitting together of the fibers into a stronger, more ho mogeneous final product.

The invention will be described further in connection with the drawing which is a flow sheet of the process of the'present invention.

We have now found that collagen fiber for particularly strong and'uniform combination with a high dissolved solids contentcollagen solution is obtained most effectively by chemical treatment of the skin or hide raw materialfor fibers to protect the fibers from excessive hydration when the raw material is subjected to subdivision in the presence of water. The fibers obtained differ from fibers obtained from untreated skin or hide material in forming a freer fibrous dispersion presumably because the surfaces ofthe fibers are not hydrated; and these freer fiberscoact with the-high dissolved solids content collagen solution to form a well knit skin-like'or leather-like sheet.

Raw material for reduction to fibers may be any skin such as a lirned unhaired hide, a pickled hide, an unlimed hide, or even a tanned hide if the tannage is such as to permit limited detannage in water. A limed hide will be washed to remove lime, with addition of some acid if necessary, to lower the pH to within the range of 7 to ll, that is, to bring the pH of the hide material to a value approaching the pH of the treating bath into which it will subsequently be put. Unlimed hide or pickled hide will normally be washed and treated with alkali to raise the pH to a value approaching the value of the chemical treating solution. Tanned hides may be subjected to suitable detanning treatment and adjusted as to pH value.

The raw material, either in the form of whole skins, scraps or in'subdivided condition, is then subjected to the chemical treatment. Since this material is to providecollagen fibers, the pieces of raw material are preferably -not smaller than 1 although products useful for some purposes may be obtained with pieces as small as A". The chemical treatment modifies the collagen fibers of the skin material to reduce their swelling tendency and to reduce the formation of gluey surfaces on the fiber material. This is most simply obtained by a limited formaldehyde treatment of the raw material in an alkaline aqueous bath. This treatment should be sufficient to provide a minimum of at least of combined formaldehyde based on the dried weight of the fibrous material and preferably not over 2% of combined substantially completely taken up the formaldehyde from solution. In a formaldehyde aqueous solution at a pH kept within the range of 9.5 to 11, substantial exhaustion of the formaldehyde will occur in 24 hours at room temperature; but no harm is done if the skin or hide is left in the solution for a longer period. A 1% formaldehyde solution a'tfa pH of 8.5 will also provide a formaldehyde content Within the desired range. Comparable modification may be obtained with other aldehydes such as glyoxal (suitably in a 3% aqueous solution at pH of 7.8 to 11) or p-quinon'e (suitably in a aqueous solution at pH 7.8 to 11).

The skin or hide may also be chemically treated with a chrome compound to achieve what amounts to a limited tanning, e.g., about chromium calculated as Cr O Excess chrome treatment, however, causes difficultyin subsequent operations and chrome treatment has not been found to achieve as satisfactory results as are obtainable by formaldehyde treatment. 7

It has also been found possible to use as raw material a mixture of chrome or vegetable tanned: scrap combined with untanned hide. In reducing this mixture of materials to fibers the mixture is beaten in an aqueous bath and it appears that the untanned hide takes up tanning agent from tanned portions of the batch, i.e., partially detans the tanned hide, and gives a mixture in which all of the fibers are tanned to a limited extent enabling separation into the constituent fibers.

Hides have been treated with a vegetable tanning agent followed by careful washing to remove excess tanning agent; but since this material tans in an acid'range It tends to detan objectionably in the neutral pH range encountered in later stages.

The subdivided hide material is mixed with water to provide a mixture containing from about 1% to about 8%, preferably about 4% solids. Lower percentages of solids may be used but cause difficulties and inefficien-.

cies in later removal of water. This mixture is sent to one or more mechanical devices involving relatively moving surfaces which exert a shearing action for pulling or. tearing the hide material into its constituent fibers and forming a pulp or suspension of the fibers in water. Suitable devices are a beater similar to that used in making paper pulp, or a, Jordan, or a plate mill in which the mixture is introduced between relatively moving rough plates which tear the material into its constituent fibers, Where a plate mill is used it has been found desirable to complete the fiber separation in a beater to avoid the roping effects sometimes encountered in a plate mill due to the twisting together of fibers.

The fiber suspension obtained may contain nubbins or small lumps particularly where the fibers are derived from a Whole skin. It is. believed that these nubbins come from the grain surface of the skin. These nubbins or lumps may, optionally, be separated from the fibers by levigation. This involves adding an emulsifying or dispersing agent, preferably a nonionic agent, to the dispersion and introducing air bubbles into the dispersion. This may be done conveniently by spraying the surface with a high velocity water jet or using an air jet. The bubbles formed attach themselves to the fibers causing them to float while the nubbins and fines sink. The fibers are skimmed off after allowing the nubbins to settle for from one to five minutes. Ionic dispersing agents may be used in this connection if salt is first added to the fiber dispersion.

is most effectively obtained from young mammalian skin, suitably a calfskin, but skins from other young ammals, such as colts or kids, may be used. The skin may be fresh, salted, or cured, for example, hide cellar scraps is a convenient source of raw material. The raw material after being washed to'rem'ove salt, dirt, or the like, is minced, for example, in a power meat grinder, to a particle size, preferably not over A"; It has been found helpful to swell the skin material in an acid bath having a pH of 3 to 5.2 for a period of, for example, six hours, before mincing the skin.

The minced or comminuted skin is dispersed in an aqueous acid bath at a pH of from 2 to 4.5. Any acid which does not precipitate protein may be used in this. step. Acetic acid at a pH of 3 to 4.5 is preferred, but formic acid, propionic acid, citric acid, phosphoric acid,

' hydrochloric acid, sulfuric acid and other common organic and mineral acids have been used. It has been found that where acetic acid at a pH of 3.2 is used this skin material does not putrefy even when kept at room temperature for. as'much as six months. The skin material is allowed to stand at a temperature below 25 C. and preferably near 0 C. in order that the acid may act uniformly on the skin. This action will have proceeded to an effective extent in from 12 to 48 hours, depending on the size of the particle, but this time may be reduced by mild agitation or stirring to as little as four hours for finely divided skin. With acids other than acetic acid a conventional bacteriostatic and/or fungistatic agent may be added if desired. The skin material should represent 5% or higher of the weight of the acid bath and desirably may be as much as 10% or more on a dry solids basis.

After acid digestion the acid bath containing skin niaterial is treated in a mechanical device to subject it to severe shearing action; A mill comprising closely spaced relatively rotating plates, e.g. a Bauer mill, has been found effective in this regard. The shearing action reduces the mixture to a heavy paste. This shearing action must be conducted under temperatures which do not cause deterioration of the acid treated skin material, i.e. at temperatures not over 25 C. The shearing action is preferably carried out at. a temperature in the neighborhood of 0 C.

After this shearing treatment, the pasty mass may be brought to a temperature below 5 C. A high percentage of collagen in this mass appears to be in solution as determined by the following test. A portion of the pasty material is diluted with a solution of the same acid r for the skin of an older calf.

The skimmed off fibers are placed on a dewatering screen and agitated to aid separation of water. The

dewatered fibers are a pulpy mass which is then passed The pasty collagen solution at 0 to 5 C. is neutralized with a suitable alkali, e.g. sodium hydroxide or potassium hydroxide, to a pH of 5.2 to 9.5, preferably about 7.5. The ionic'strength of the neutralized collagen solution is adjusted by. addition of salt to give an ionic strength such that aftermixture with hide fiber material, the ionic strength of the mixture will be in the range of from 0.1 to 0.5.

form satisfactorily.

*The following is the formula employed to derive -the value of ionic strength:

Ionic strength molarity (of each ion) va1ence (of each ion) To adjust the ionic strength, the normal additive is sodium chloride, but other inorganic salts such as sodium sulfate and potassium chloride are useful. Salts of which the cations are known to precipitate collagen are excluded and the borates and carbonates have been found to interfere with the process.

Basic agents useful to neutralize the material include NaOH, KOH, Na PO Na HPO ammonia, organic amines and so on. Buffer salts may be employed to aid in providing a closer control of the final pH.

The cooled, neutralized, ionic strength adjusted collagen gel is then mixed with cooled hide fiber. This mixing involves tearing apart or otherwise separating portions of the pressed sheet of hide fibers and introducing these portions into the collagen gel in a mixer. On a solids basis the fibers and gel are usually combined in proportions to give about 5% to 15% gel solids based on the total solids of the mixture. As low as 1% gel solids will give a useful sheet material and up to as high as- 50% collagen gel solids is considered useful.

Y A humectant softener or plasticizer, suitably an aliphatic polyhydroxy compound, for example sorbitol or glycerine, may be incorporated in the collagenous matereial if desired. The amount of softener or plasticizer incorporated will depend upon the resultants desired in the final product and may be, for example, in the range of from 1% to 10% based on the weight of the fluid or paste. The softener or plasticizer is incorporated by suitable mechanical mixing means.

The mixing of the cooled collagen solution and fibers is efi'ected in a suitable jacketed mixing and kneading machine which will maintain the temperature of the mixture at from to C. and which will work together the fibers and the'collagen solution without Winding up ropes of fiber on the agitator. A mixing and kneading machine using a solid worm type agitator has been found effective. Mixing is continued until the product is uniform and free from lumps. Using a solid worm type mixer, this state has been obtained in about /2 hr. The product is a mass which resembles a dough in its resistance to extreme deformation.

From the mixer, the heavy doughy mass is discharged and worked into a sheet. This sheet may be rolled to a determined thickness using a roller supported in spaced relation to a forming surface by guide strips. The thickness of the sheet of the doughy mass is chosen depending on the desired final thickness. For example, a wet doughy sheet .43 thick will give a final sheet product of from 0.050" to 0.055", which indicates a shrinkage of about /2. The forming surface may be embossed providing a desired surface pattern on the sheet formed thereon.

The formed sheet is then raised to a temperature up to 37 C. until fiber formation has occurred. The warming technique is the same as used in the above referred to application. To provide a surface corresponding to the grain surface on a sheet of leather, the wet sheet before being warmed may be coated or brushed with collagen solution. in the course of warming, collagen fiber from this portion, which is locally more concentrated in collagen, developed as a fine interconnected fiber network providing a tightly knit fibrous grain surface,

-After-thesheethas been warmed and the collagen fibers reconstituted, the sheets mayibe subjected tovarious treatments. For example, the sheets maybe dried in solvent and then tanned in an aqueous tanning bath in accordance with standard tanning procedure. Alternatively, the wet sheets may be pressed to remove excess water and put directly in an aqueous tanning bath. The sheets may be impregnated with a softener suitably an aliphatic polyhydroxy compound. In drying of wet sheets of the collagen fibers, the edges of the sheets may be held to prevent shrinkage in area.

The following example is given to aid in understanding the invention and it is tobe understood that the invention is not limited to .the materials, reagents, or procedural details of the example:

Example 120 lbs. of trimmings from green salted light (4-6 lb.) calfskins were placed in a drum and washed in running cold water at a drum speed of about 12 r.p.m. for about 12 hours to remove the salt. The trimmings were then drained and passed through a plate-type meat grinder of which the plate had circular holes. The ground material was washed and drained, and the drained mass weighed about 80 lbs.

To the washed and drained mass 2.5 lbs. of glacial acetic acid were added and vigorously stirred in. The acidified mass had a pH of about 3. 75 and a dry solids content of about 10%, and was allowed to stand at room temperature for two days.

After standing the acidified skin material wascooled by mixture with chipped ice and passed through a platetype shearing mill of which the plates had an edgeclearance of about 0.005" to 0.010. The material left the mill as a smooth paste whitened by occlusion of fine air bubbles. On standing the air bubbles became aggregated, absorbed, or removed, leaving an opaque, tan-colored paste having a solids content of about 7%.

Trimmings from limed steer hides were washed in a rotating drum (12 r.p.m.) for two hours in running tap water. lbs. of the washed trimmings were placed in 20 gal. of water and 400 ml. of glacial acetic acid were added and thoroughly stirred in to partially neutralize the trimmings. A cut section of the trimmings showed a pH of about 4. The trimmings were again washed with running water in a drum for a period of about 1 /2 hours and thereafter were drained. An aqueous solution of 6.25 lbs. of a wetting agent in 6.25 lbs. of water at 30 C. were added to the trimmings and drummed in.

drumming until the efiluent was clear. The trimmings were drained. Thereafter 30 gal. of water and 2850 ml. of 37% aqueous formaldehyde solution were drummed into the trimmings for 30 minutes. The trimmings were then removed, placed in a prepared mixture of 20 gal. of water and 1900 ml. of 37% aqueous formaldehyde solution and stirred to effect a uniform mixture. The pH of the mixture was brought to about 8 by the addition of 54 grams of sodium hydroxide and the material was allowed to stand for 5 days. The trimmings were then Washed in the drum in running water for 2 hours. The material was cut into 1" strips and then passed through a plate-type meat grinder having 6 holes. The ground material was drained and introduced into a Hollander paper heater in which the material was beaten for 10 to 15 minutes after the bumping, due to the presence of large lumps had stopped. The beaten material which was 'a uniform suspension of hide fibers was drained on a 20 mesh screen. The mass of drained fibers was then passed between tightly pressed rubber rolls to remove additional water. At this point the formaldehyde content of the fibers was about 1% on a dry solids basis; and the dry solids content was mass.

Thereafter, water at 30 C. was intro duced into the drum and washing was continued with 7 about 25% of the pressed fiber "7 2,030 grains of the acidified calfskin material 'was placed in a 1 gal. jar, and cooled by addition of about 1000 grams of chipped ice to between and C. 46.98 grams of K HPO in about 200 ml. of water'was' added and mixed in thoroughly and the mixture was then' neutralized with about 125 ml. of .6 N KOH to give a pH of about 7.5. Ice and water were added to bring the volume of the mixture to 1 gal. and the final mixture to an ionic strength of about 0.4. 1333 grams of this chilled neutral mass was placed in a screw-type, jacketed mixer which had been precooled to from 0 to 2 C. by circulating a salt and ice brine through the jacket. The mixer was started and 1136 grams of the pressed fiber was introduced slowly in small bits torn frornthe mass of fibers. The material was pressed down in close contact with the screw of the mixer and subjected to mixing for a period of about one hour until the 'mass was asmooth, uniform paste which was doughy in its resistance to extreme deformation. The mixture was taken from the mixer and rolled into a sheet A thick using rolling strokes, first in one direction and then in a direction perpendicular to the first direction in order to move the fiber-containing mixture uniformly in all directions in theplane of the sheet. The mixture was kept below5 C. from the time when it was first prepared until rolling was completed.

The rolled out sheet was covered by spreading a thin polyethylene film into close contact with its exposed surface. The sheet was then warmed to 37 C. slowly and held at this temperature for one hour. At the end of the heating the dissolved collagen content of the paste had reconstituted as fibers and the sheet could be handled without support.

The sheet was pressed between absorbent felts at a pressure of about 50 lbs. per sq. inch and dried 'by immersion in acetone for a period of about 4 hrs. On removal from the acetone and evaporation of the impregnating acetone the product was a white porous sheet about 0.06" in thickness.

Having described our invention, what we claim as new and desire to secure by Letters Patent of the United States is: 1'. A method for forming interlocked collagen fiber masses comprising the steps of lightly tanning skin to inhibit hydration of the fibers of the skin, placing said skin in water, tearing said skin into fibers suspended in said water, separating the fibers from a major portion of the water, forming a mixture of said fibers and an aqueous solution of collagen, said mixture'having an ionic strength of 0.1 to 0.5 and a pH of from about 5.2 to about 9.5 and being formed and maintained at a temperature below about 5 C. to prevent precipitation of collagen, and warming the resultant mixture to a temperature below 37 C. sufficient to precipitate collagen fibers from said collagen solution in interlocking relation with said skin fibers.

2. A method for forming interlocked collagen fiber masses comprising thesteps of lightly tanning skin to inhibit hydration of the fibers of the skin, placing said skin in water, tearing said skin into fibers suspended in said water, separating the fibers from a major portion of the water, cooling said fibers to below about 5 C., mixing the fibers with an aqueous solution of collagen, said solution of collagen having an ionic strength and pH which after mixture with said fibers will be in the range of from about 0.1 to 0.5 ionic strength and pH of from about 5.2 to about 9.5 and being maintained at a. temperature below about 5 C. to prevent precipitation of collagen, and warming the resultant mixture to a temperature below 37 C. suificient to precipitate collagen fibers from said collagen solution in interlocking relation with said skin fibers.

e 3. A method for forming interlocked collagen fiber masses comprising thesteps of lightly tanning said skin with formaldehyde to inhibit hydration of the collagen fibers of the skin, placing said skin in water, subjecting said skin to shearing force between relatively moving surfaces to tear said skin into fibers and disperse said fibersoin water, separating thefibers from a major portion of. the water, coolingsaid fibers to below about 5 C., mixing the fibers with an aqueous solution of collagen,

said solution of collagen having an ionic strength and pH which after mixture with said fibers will be in the range of from about 0.1 to 0.5 ionic strength and a pH of from about 5.2 to 9.5 and being maintained at a temperature below about 5 C. to prevent precipitation of collagen, and warming the resultant mixture to a temperature from below 37 C. sufiicient to precipitate col.

lagenfibers from said collagen solution in interlocking relation with said skin fibers.

4. The method for forming interlocked collagen fiber masses comprising the steps of lightly tanning said skin with formaldehyde, placing said skin in water, subjecting said skin to shearing force between relatively moving surfaces to tear said skin into fibers and disperse said fibers in said water, separating said fibers from a major portion of said water, comminuting young mammalianskin, soaking the comminuted skin in aqueous acid solution at a pH of from about 2 to 4.5 to swell and at least partially dissolve said comminuted skin, subjecting said comminuted skin to shearing action to im-.

pH of the collagen solution to values which after subse.

quent mixture of said solution with said fibers will be in the range of from about ionic strength 0.1 to 0.5 and pH of from about 5.2 to 9.5 while maintaining the solution'at a temperature not over about 5 C. to prevent precipitation of collagen, cooling said fibers to below about 5 C., intimately mixing said fibers and said collagen solution, spreading said mixture in a layer, warming said layer to a temperature not higher than 37 C. sufiicient to precipitate collagen fibers from said collagen solution and to form a gel, and removing fluid from said gel to reduce it to a body of interlocked collagen fibers.

5. The method for forming interlocked collagen fiber V masses comprising the steps of immersing skin in an aqueousalkaline solution of formaldehyde to secure a combined formaldehyde content in said skin of from about 0.75% to 1.5% by weight based on the dry weight of said skin, removing said skin from said solution, placing said skin' in water, subjecting said skin to shearing force between relatively moving surfaces to tear said skin into fibers and disperse said ,fibers in said water, separating said fibers from a major portion of said water, comminuting young mammalian skin, soaking the comminuted skin in aqueous acetic acid solution at a pH of from about 3 to 4.5 to swell and at least partially dissolve said comminuted skin, subjecting said comminuted skin to shearing action to improve solution of its collagen content, cooling the resultant collagen solution and maintaining it at a temperature not over about 5 C., adding a salt and a bufiering agent to the collagen solution to bring the ionic strength and pH of the collagen solution to values which after subsequent mixture of said solution with said fibers will be in the range of from about ionic strength 0.1 to 0.5 and pH of from about 5.2 to 9.5 while maintaining the solution at a temperature not over about 5 C. to prevent precipitation of collagen, cool ing said fibers to below about 5 C., intimately mixing said fibers and said collagen solution, spreading said mixture in a layer, warming said layer to a temperature not higher than 37 C. sufiicient to precipitate collagen fibers from said collagen solution and to form a gel, and removing fluid from said gel to reduce it to a body of interlocked collagen fibers.

-6. The method for forming interlocked collagen fiber masses comprising the steps of immersing; skin in an aqueous alkaline solution of formaldehyde to secure a combined formaldehyde content'i'n said skin of from about 0.75% to 15% by weight based on the dry-weight of said skin, removing said skin from said solution, placing said skin in water, subjecting said skin to shearing force between relatively moving surfaces to tear said skin into fibers and disperse said fibers in said water, separating said fibers from a major portion of said water, comminuting calfskin, soaking the comminuted skin in aqueous acetic acid solution at a pH of from about 3 to 4.5 to swell and at least partially dissolve saidcomminuted skin, subjecting said comminuted skin to shearing action to improve solution of its collagen content, cooling the resultant collagen solution and maintaining it at a temperature not over about 0., adding a salt and a bufl ering agent to the collagen solution to bring the ionic strength and pH of the collagen solution to values which after subsequent mixture of said solution with said fibers will be in the range of from about ionic strength 0.1 to 0.5 and pH of about 7.5 While maintaining the solution at a temperature not over about 5 C. to prevent precipitation of collagen, cooling said fibers to below about 5 C., intimately mixing said fibers and said collagen solution in relative proportions to provide from about 1% to about 50% of dissolved collagen solids based on the total solids of the mixture, spreading said mixture in a layer, warming said layer to a temperature not higher than 37 C. sufficient to precipitate collagen fibers from said collagen solution and to form a gel, and

removing fluid from said. gel to reduce it to a body of interlocked collagen fibers.

7. The method for forming interlocked collagen fiber masses comprising the steps of immersing skin in'an aqueous alkaline solution of formaldehyde to secure a combined formaldehyde content in said skin of from about 0.75% to 1.5% by weight based on the dry Weight of said skin, removing said skin from said solution, placing said skin in water, subjecting said skin to shearing force between relatively moving surfaces to tear said skin into fibers and disperse said fibers in said water, removing nubbins from the resulting fiber dispersion, separating said fibers from a major portion of said water, comminuting calfskin, soaking the comminuted calfskin in aqueous acetic acid solution at a pH of from about 3 to 4.5 to swell and at least partially dissolve said comminuted skin, subjecting said comminuted skin to shear- ,iug action to improve solution of its collagen content,

cooling the resultant collagen solution and maintaining it at a temperature not over about 5 C., adding a salt and a buffering agent to the collagen solution to bring the ionic strength and pH of the collagen solution to values which after subsequent mixture of said solution with said fibers will be in the range of from about ionic strength 0.1 to 0.5 and pH of about 7.5 while maintaining the solution at a temperature not over about 5 C. to prevent precipitation of collagen, cooling said fibers to below about 5 C., intimately mixing said fibers and said collagen solution in relative proportions to provide from about 1% to about 50% of dissolved collagen solids based on the total solids of the mixture, spreading said mixture in a layer by pressure applied to cause flow approximately uniformly in all directions in the plane of the sheet, warming said layer to a temperature not higher than 37 C. suflicient to precipitate collagen fibers from said collagen solution and to form a gel, removing fluid from said gel to reduce it to a body of interlocked collagen fibers, impregnating said layer with a softener, holding the edges of said layer to prevent shrinkage in area of said layer, and drying said layer.

8. The method for forming interlocked collagen fiber masses comprising the steps of immersing skin in an aqueous alkaline solution of formaldehyde to secure a combined formaldehyde content in said skin of from about 0.75% to 1.5% by weight based on the dry weight of said skin, removing said skin from said solution, plate ing said skin in water, subjecting said skinto shearing force between relatively moving surfaces to tear said skin into fibers and disperse said fibers in said water, removing nubbins from the resulting fiber dispersion, sep a' rating said fibers from a major portion of said Water, comminuting calfskin, soaking the comminuted skin in aqueous acetic acid solution at a pH of from about 3 to 4.5 to swell and at least partially dissolve said comminuted skin, subjecting said comminuted skin to shearing action to improve solution ofits collagen content, cooling the resultant collagen solution and maintaining it at a temperature not over about 5 C., adding a salt and a buffering agent to the collagen solution to bring the ionic strength and pH of the collagen solution to values which after subsequent mixture of said solution with said fibers will'be in the range of from about ionic strength 0.1 to

0.5 and pH of about 7.5 while maintaining the solution at a temperature not over about 5 C. to prevent precipitation of collagen, cooling said fibers to below about' 5 C., intimately mixing said fibers and said collagen solution in relative proportions to provide from about 1% to about 50% of dissolved collagen solids based on the total solids of the mixture, spreading said mixture in a layer by pressure applied to cause flow approximately uniformly in all directions in the plane of the sheet, coating the surface of said sheet with a further portion of said collagen solution, warming said layer to a temperature not higher than 37 C. sufficient to precipitate collagen fibers from said collagen solution and to form a gel, removing fluid from said gel to reduce it to a body of interlocked collagen fibers, impregnating said layer with an aliphatic polyhydroxy compound, holding the edges of said layer to prevent shrinkage in area of said layer, and drying said layer.

9. The method for forming interlocked collagen fiber masses comprising the steps of mixing pieces of tanned and untanned skin, placing the mixed skins in water, subjecting said mixed skins to shearing force between relatively moving surfaces to tear said skin into fibers, to disperse said fibers in said water, and to effect partial interchange of tanning agent from tanned skin to untanned skin, separating said fibers from a major portion of said water, comminuting young mammalian skin, soaking the comminuted skin in aqueous acid solution at a pH of from about 2 to 4.5 to swell and at least partially dissolve said comminuted skin, subjecting said comminuted skin to shearing action to improve solution of its collagen content, cooling the resultant collagen solution and maintaining it at a temperature not over about 5 C., adding a salt and a buffering agent to the collagen solution to bring the ionic strength and pH of the collagen solution to values which after subsequent mixture of said solution with said fibers will be in the range of from about ionic strength 0.1 to 0.5 and pH of from about 5.2 to 9.5 while maintaining the solution at a temperature not over about 5 C. to prevent precipitation of collagen, cooling said fibers to below about 5 C., intimately mixing said fibers and said collagen solution, spreading said mixture in a layer, warming said layer to a temperature not higher than 37 C. sufficient to precipitate collagen fibers from said collagen solution and to form a gel, and removing fluid from said gel to reduce it to a body of interlocked collagen fibers.

10. The method for forming interlocked collagen fiber masses comprising the steps of mixing pieces of tanned and untanned skin, placing the mixed skins in water, subjecting said mixed skins to shearing force between relatively moving surfaces to tear said skin into fibers, to disperse said fibers in said water, and to effect partial in terchangc of tanning agent from tanned skin to untanned skin, separating said fibers from a major portion of said water, comminuting calfskin, soaking the comminuted skin in aqueous acetic acid solution at a pH of from about 3 to 4.5 to swell and at least partially dissolve said comrninuted skin, subjecting said comminuted skin to shearing action to improve solution of its collagen content, cooling the resultant collagen solution and main-' taining it at a temperature not over about 5 C., adding a salt and a buffering agent to the collagen solution to bring the ionic strength and pH of the collagen solution to values which after subsequent mixture of said solution with said fibers will be in the range of from about ionic strength 0.1 to 0.5 and pH of about 7.5 while maintaining the solution at a temperature not over about 5 C. to prevent precipitation of collagen, cooling said fibers to below about 5 C., intimately mixing said fibers and said collagen solution in relative proportions to provide from about 1% to about 50% of dissolved collagen solids based on the total solids of the mixture, spreading said mixture in a layer, Warming said layer to a temperature not higher than 37 C. sufiicient to precipitate collagen fibers from said collagen solution and to form a gel, and removing fluid from said gel to reduce it to a body of interlocked collagen fibers.

11'. A porous" animal skin-like mass consisting essentially ofinterlocked structured collagen fibers knitted togetherinfla randomly interwoven three-dimensional network and comprising both collagen fibers derived directly from lightly tanned skin, and collagenfibers formed on said directly derived fibers by precipitation from collagen solution.

References Cited in the file of this patent UNITED STATES PATENTS 1,728,39l Christensen Sept. 17, 1929 2,158,265 Wilson May 16, 1939 2,631,942 Highberger Mar. 17, 1953 2,838,363 Veis et a1. June 10, 1958 MWMCSEAL) UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N z ese am April 26 1960 John H. Highberger et al,

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4 line 50 for "0.3%" read O2% column. 5

line 36 for resultants" read results ==-=g column 8 line l3 strike out "from"..

Signed and sealed this 1st day of November 1960o Attcst:

KARL H. AXLINE ROBERT C. WATSON Attesting Oflicer Commissioner of Patents 

1. A METHOD FOR FORMING INTERLOCKED COLLAGEN FIBER MASSES COMPRISING THE STEPS OF LIGHTLY TANNING SKIN TO INHIBIT HYDRATION OF THE FIBERS OF THE SKIN, PLACING SAID SKIN IN WATER, TEARING SAID SKIN INTO FIBERS SUSPENDED IN SAID WATER, SEPARATING THE FIBERS FROM A MAJOR PORTION OF THE WATER, FORMING A MIXTURE OF SAID FIBERS AND AN AQUEOUS SOLUTION OF COLLAGEN, SAID MIXTURE HAVING AN IONIC STRENGTH OF 0.1 TO 0.5 AND A PH OF FROM ABOUT 5.2 TO ABOUT 9.5 AND BEING FORMED AND MAINTAINED AT A TEMPERATURE BELOW ABOUT 5*C. TO PREVENT PRECIPITATION OF COLLAGEN, AND WARMING THE RESULTANT MIXTURE TO A TEMPERATURE BELOW 37*C. SUFFICIENT TO PRECIPITATE COL- 